1. Field of the Invention
The present invention relates to a semiconductor memory and, more particularly, to a semiconductor memory, which can be used as a file device serving as an alternative for a floppy disk, a hard disk, or the like in information equipment such as a computer.
2. Description of the Related Art
Conventionally, a semiconductor memory is manufactured under an assumption that it is used as a main memory for, e.g., a computer, and can be directly accessed from a CPU. More specifically, an address signal generated by a CPU is connected to an address signal of a semiconductor memory, thereby directly addressing the memory. FIG. 1 shows a typical arrangement of I/O pins of such a conventional semiconductor memory.
A semiconductor memory shown in FIG. 1 has a memory capacity of 4 Mbits (512K.times.8 bits), and is constituted by a package having 32 pins, as shown in FIG. 1. Of the 32 pins, 19 pins are address input terminals for receiving address signals A0 through A18. In this manner, the conventional semiconductor memory requires special-purpose address input terminals corresponding in number to its memory capacity.
For this reason, when the memory capacity of a semiconductor memory is increased to 8, 16, or 64 Mbits in future, the number of address input terminals is increased accordingly. Therefore, the size of the package for storing the semiconductor memory is increased. As a result, a mounting space on a printed circuit board on which the package is mounted is also increased.
Therefore, the arrangement of the conventional semiconductor memory premised on direct addressing from the CPU is suitable for a case wherein the CPU executes a program, and a case wherein the CPU directly accesses data in the memory. However, when the semiconductor memory is used as a file device requiring a large memory capacity such as a floppy disk, a hard disk, or the like, it poses a problem about its mounting space.
The direct addressing method from the CPU is advantageous for a high-speed access. However, since the direct addressing method occupies a memory address space of the CPU, it undesirably oppresses the address space of the main memory. For this reason, when the semiconductor memory is used as a file such as a floppy disk, a hard disk, or the like, the addressing method is preferably realized by an I/O access method. In the I/O access method, an address counter for storing addresses of the semiconductor memory is allocated in an I/O space of the CPU, and an address to be accessed of the semiconductor memory is written in the counter so as to perform a read or write operation.
However, when the semiconductor memory shown in FIG. 1 is to be accessed by the I/O access method, a control circuit such as an address circuit must be realized outside the semiconductor memory. When a file device is constituted by, e.g., a memory board mounting a plurality of semiconductor memories, a control circuit must be prepared in consideration of the memory capacities of the memories, and the number of mounted memories, and the like. As a result, the arrangement of the control circuit becomes complicated.